Since the careful pioneer work of Zeller (1872, 1876), Polystoma integerrimutn has drawn the attention of a number of workers, and this species is probably the best known of the Monogenetic trematodes. However, certain important inconsistencies have arisen in the literature on Polystoma integerrimum and related forms, particularly in the description of the genital system; in view of this a reinvestigation of the anatomy of this species was undertaken.